The present invention relates to identifying flaws in a magnetic storage system. In particular, the present invention relates to identifying flaws by monitoring the location of window edges in a readback signal of a magnetic storage system.
In a magnetic storage system, such as a computer disc drive, digital information is magnetically i0 stored upon the surface of a magnetic disc. The digital information is represented by seleotivelY polarizing the magnetic field of consecutive areas across the surface of the rotating magnetic disc. When this information is read back from the storage disc, the magnetic polarization of the medium is sensed and converted into an electrical output signal. This reading and writing operation is through a magnetic read/write head which is suspended over the surface of the rotating disc and which provides a raw data signal. The raw data signal is representative of relative strength of the magnetic flux density present on the magnetic disc. It is highly desirable to provide the highest level of information storage density possible for a given magnetic storage system. Unfortunately, increased storage density leads to significant noise levels in the raw data signal.
The raw data signal comprises a series of data "peaks" whose location is used to represent digital information. With high data storage densities, the precise location of a data peak becomes critical because adjacent data peaks are spaced very close together. If a data peak is shifted slightly in time, incorrect information may be read back. This causes a bit shift error in the digital data signal.
Flaws in the magnetic storage medium may induce shifts in the edges of the data peaks. Severe shifts may result in errors during readback of magnetically encoded information. When manufacturing a disc drive system, it is critical that the manufacturer be able to measure bit shift for a given head/disc combination at the desired storage density. This measurement is used to certify the storage system, guaranteeing a maximum error rate at the specified data storage density. Furthermore, if a magnetic storage medium has a small number of localized flaws, it is possible to map out the defective areas on the surface. of the storage medium. Typically, a map is generated during manufacture of the storage system. The map is stored in a disc controller. During operation, the map is used to identify flawed sectors in the disc surface. The flawed disc sectors are not used for information storage.
A simple and accurate method and apparatus for locating flaws in the surface of magnetic storage media would be a significant contribution to the art.